The invention relates to a motion device formed by a flat actuating coil (e.g. a Lorentz voice coil) positioned between magnets having improved rattle space, a joystick with improved geometry incorporating the motion device and to an optical position sensing system
A number of active joysticks or haptic interfaces (interfaces capable of generating kinesthetic and tactile feedback to the user) have been proposed for virtual environments and teleoperation systems.
Attention is directed to Stocco, L., Salcudean, S. E., xe2x80x9cA coarse-fine approach to force-reflecting hand-controller design,xe2x80x9d in Proc. 1996 IEEE Intl. Conf. Rob. Aut. Minneapolis, MN, pp.xcx9c404-410, Apr. 22-28, 1996. for a detailed survey, and to Hayward, V., Astley, O. R., xe2x80x9cPerformance measures for haptic interfaces,xe2x80x9d in Proc. ISRR, p.xcx9c(12 pages), 1995. for performance measures.
The need for high acceleration in haptic computer-user interfaces has been demonstrated in many studies and seems to have been accepted by designers. Although most reported designs have translational workspaces that exceed a cube with 10 cm sides, it has not been shown that a workspace of this magnitude is really needed. Indeed, for desk-top computing, input devices such as mice, trackballs or joysticks are commonplace. These devices have relatively small motion ranges to avoid tiring the operator. Furthermore, designing high acceleration devices over large workspaces is a non-trivial task requiring expensive actuators, transmissions and joints.
As an alternative, the use of a small workspace haptic device in rate mode or combined position/rate mode has been proposed and demonstrated see Salcudean, S. E., Wong, N. M., Hollis, R. L., xe2x80x9cDesign and Control of a Force-Reflecting Teleoperation System with Magnetically Levitated Master and Wrist,xe2x80x9d IEEE Trans. Rob. Aut., vol.xcx9c11, pp.xcx9c844-858, December 1995.
Magnetically levitated (maglev) Lorentz devices such as those described in Hollis, R. L., Salcudean, S. E., Allan, P. A., xe2x80x9cA six degree-of-freedom magnetically levitated variable compliance fine motion wrist: Design, modeling and control,xe2x80x9d IEEE Trans. Rob. Aut., vol.xcx9c7, pp.xcx9c320-332, June 1991 and U.S. Pat. No. 5,146,566, issued September, 1992 to Hollis, R. L. and Salcudean S. E are suitable small-motion haptic interfaces because of their low mass, lack of friction and backlash, and high acceleration ability. Devices have been built at IBM (see Hollis, R. L., Salcudean, S. E., Allan, P. A., xe2x80x9cA six degree-of-freedom magnetically levitated variable compliance fine motion wrist: Design, modeling and control,xe2x80x9d IEEE Trans. Rob. Aut., vol.xcx9c7, pp.xcx9c320-332, June 1991); at University of British Columbia (see Salcudean, S. E., Wong, N. M., Hollis, R. L., referred to above), and at Carnegie-Mellon University (see Berkelman, P. J., Butler, Z. H., Hollis, R. L., xe2x80x9cDesign of a hemispherical magnetic levitation haptic interface device,xe2x80x9d in Proc. 1996 ASME IMECE, vol.xcx9cDSC-58, Nov. 17-22, 1996).
In such devices magnetic forces are used to actively levitate a rigid mass or flotor to which the handle manipulated by the operator is attached. These devices share the following three subsystems:
(i) an actuation system consisting of at least six flat voice-coil or Lorentz actuators,
(ii) an optical position sensing system consisting of infrared linear light rays projecting from light-emitting diodes or lasers onto two-dimensional lateral effect photodetectors or position sensing diodes,
(iii) a control system that commands forces and torques to the actuation system based on the desired and sensed position, the desired force and the desired relationship between force and position (mechanical impedance).
A number of applications of maglev devices are described in the survey paper Hollis, R. L., Salcudean, S. E., xe2x80x9cLorentz levitation technology: a new approach to fine motion robotics, teleoperation, haptic interfaces, and vibration isolation,xe2x80x9d in Proc. 5th Intl. Symp. on Robotics Research, (Hidden Valley, Pa.), p.xcx9c(18 pages), Oct. 1-4, 1993.
U.S. Pat. No. 5,790,108 issued to Salcudean et al. on Aug. 4, 1998 describes a specific application of the Lorentz voice coils in a hand controller.
It is object of the present invention to provide voice-coil actuators with significantly larger xe2x80x9crattle spacexe2x80x9d or significantly higher forces for a given xe2x80x9crattle spacexe2x80x9d.
Broadly the present invention relates to a basic actuator structure comprising a stator formed by a pair of opposed magnets defining a gap therebetween a floater formed by a flat actuator coil interposed in the gap. The gap has a width d and the flat coil has a thickness dc and the ratio of coil thickness dc to gap width d is between ⅓ and xc2xd (dc/d=⅓ to xc2xd) to provide a larger rattle space without sacrificing force applied between the coil and magnets.
It is a further object of the present invention to provide a new actuation system geometry, providing a well conditioned transformation from actuator currents to resultant forces and torques, to produce uniformly distributed commanded forces and torques,
Broadly the present invention relates to a joystick structure comprising a stator formed by an outer cage with an internal cube shaped compartment and a cube mounted within the compartment with each cube face of said cube in opposed relation with a corresponding face of said compartment, opposing pairs of magnet assemblies one magnet assembly of each pair mounted on a cube face and the other on the corresponding opposed face of said compartment, each said pair of magnet assemblies defining a gap therebetween, a flotor formed by a plurality of flat actuating coils held in fixed relationship with respect to each other and positioned one of said coils in each of said gaps, said magnetic assemblies on three of said cube faces forming a vertex being oriented with their longitudinal axes substantially parallel to the cube diagonals emanating from said vertex, and said assemblies on the remaining three of the cube faces forming an opposite vertex being oriented with their longitudinal axes substantially perpendicular to the cube diagonals emanating from said opposite vertex and each said coils having their longitudinal axes substantially parallel to the longitudinal axis of said pair of magnet assemblies between which it is interposed.
Preferably said stator compartment and said cube are arranged with one of their major diagonal axes substantially vertical.
It is yet another objective of the present invention to provide a new optical position sensor that is significantly less expensive than sensing systems used in other maglev devices, even though it provides similar sensing volume and resolution.
Broadly the present invention relates to an optical position sensor comprising at least one linear position-sensing diode mounted on one of a stator or a floater and a plurality of planar light beam projectors on the other of the stator and flotor with the light beam projectors projecting light beams at an angle to each other, said angle being greater than zero and said light beams traversing said at least one linear light position sensor at a plurality of spaced locations when in a field of operation of said optical position sensor and means for separately identifying said light beams.
Preferably said means for separately identifying said light beams is selected from the group of means for activating said light beams one at a time and means for varying intensities of said light beams at different frequencies.
Preferably said linear light position sensor are mounted in the same plane.
Preferably said plurality of planar light beams comprises two and said two light beams are substantially perpendicular.
Preferably said linear light position sensors are arranged in a plane as a triangle and said plurality of light beams comprises three planar light beams arranged to project light along the adjacent faces of a pyramid with its vertex pointing towards said plane and projecting a light triangle onto said plane.
Preferably said linear light position sensor triangle is substantially equilateral and said pyramid is substantially a cubic pyramid.
Preferably said light is infrared light.